Two-Part Cyanoacrylate Curable Adhesive System

ABSTRACT

Two-part cyanoacrylate/cationically curable adhesive systems are provided.

BACKGROUND Field

Two-part cyanoacrylate curable adhesive systems are provided.

Brief Description of Related Technology

Curable compositions such as cyanoacrylate adhesives are well recognisedfor their excellent ability to rapidly bond a wide range of substrates,generally in minutes and depending on the particular substrate, often ina number of seconds.

Cationically curable compositions generally are well known, inparticular epoxy compositions which are widely used. Epoxy compositionsonce cured are known to form robust bonds between substrates made frommany different types of materials. However, epoxy compositions, whetherin one or two-parts, do not have anywhere near the same rapid fixturetime shown by cyanoacrylates, and may tend to show poor performanceproperties on substrates constructed from certain materials inparticular plastic substrates, such as polycarbonate (PC),acrylonitrile-butadiene-styrene copolymer (ABS), polymethylmethacrylate(PMMA), and polyvinyl chloride (PVC) to name a few.

Two-part compositions comprising cyanoacrylate and an epoxy provide goodperformance across substrates constructed from a wide variety ofmaterials and provide improved durability performance over conventionalcyanoacrylate compositions and improved fixture time and improvedplastic bonding over conventional cationically curable compositions. Forexample International Patent Application Publication No. WO2014/140804describes two-part cyanoacrylate/cationically adhesive systems,comprising a first part comprising a cyanoacrylate component and acationic catalyst and a second component comprising an epoxy component.The adhesive systems described therein demonstrated an ability to bond awide variety of substrates.

Notwithstanding the excellent properties of two-part cyanoacrylate/epoxycompositions there may be on occasion mixing issues wherein thetwo-parts of the composition are not mixed in the correct ratio, duringapplication of the composition through a mixing nozzle, as there may bea large viscosity difference between the two-parts of the composition,i.e., the viscosity of the cyanoacrylate component is oftensignificantly less than that of the epoxy component.

The lower viscosity of the cyanoacrylate component may also result insag of the composition, that is, the composition may deform and loseshape under the compositions own weight prior to curing of thecomposition.

Conventional thixotropic agents, such as fumed silica, are generallyknown in the art. For example the epoxy component of prior art two-partcompositions may comprise a thixotropic agent, such as fumed silica, toincrease the viscosity of the epoxy component.

Conventional thixotropic agents are generally compatible withcyanoacrylate compositions, however in two-part systems wherein thecyanoacrylate further comprises a cationic catalyst conventionalthixotropic agents, such as fumed silica, tend to make the cyanoacrylatecomponent unstable, leading to gelation of the cyanoacrylate component.

It would be desirable to provide an adhesive system having both thefeatures of an instant cyanoacrylate adhesive, such as fast fixturetimes and the ability to bond a wide range of substrates such as metalsand plastics, together with the robust strength seen with epoxycompositions.

SUMMARY

In one aspect, the present invention provides a two-part curablecomposition comprising:

-   -   (a) a first part comprising a cyanoacrylate component, a        cationic catalyst, and a plurality of polyolefin fibres;    -   (b) a second part comprising a cationic curable component, and        an initiator component;        wherein when said parts are mixed together, the cationic        catalyst initiates cure of the cationic curable component.

Significantly the polyolefin fibres increase the viscosity of the firstpart of the composition without affecting stability of the first part ofthe composition.

Suitably, the first part has an initial viscosity from about 6,000 mPa·sto about 16,000 mPa·s, when measured at 25° C. and wherein the firstpart has a viscosity of from about 12,000 mPa·s to about 48,000 mPa·s,when measured at 25° C., after aging for 72 hours at 82° C. Thisadvantageously facilitates optimal mixing of the first and second parts.

Suitably, the polyolefin fibres are high density polyethylene.

The polymeric fibres may have an average length of from about 400 μm toabout 1000 μm. Optionally the polymeric fibres may have an averagelength of from about 600 μm to about 800 μm. The polymeric fibres mayhave an average diameter of more than about 5 μm and less than about 25μm, e.g., from about 10 μm to about 20 μm.

Suitably, the viscosity of the second part is in the range of from about20,000 to about 40,000 mPa·s, when measured at 25° C. Advantageously,the viscosity of the second part remains in this range over time.

Preferably, the viscosity of the first part when measured at 25° C.,after ageing for 72 hours at 82° C., is less than about three times theinitial viscosity of the first part when measured at 25° C.

Advantageously, when the viscosity of the first part is in the range offrom about 12,000 mPa·s to about 48,000 mPa·s, when measured at 25° C.,after ageing for 72 hours at 82° C., optimal mixing is achieved whencombined with Part B.

Suitably, the polyolefin fibres are present in an amount of from about0.1 wt % to about 5 wt % based on the total weight of the first part,such as from about 0.5 wt % to about 3.5 wt % based on the total weightof the first part, for example from about 0.5 wt % to about 2.5 wt %based on the total weight of the first part, of the two-partcomposition.

The two-part curable composition may further comprising core-shellrubber particles comprising acrylonitrile butadiene-styrene copolymerand/or methyl methacrylate butadiene styrene copolymer.

Optionally, the core-shell rubber particles may be present in an amountof from about 0.1 to about 5 weight percent, in the first part of thecomposition, based on the total weight of the first part of thecomposition.

Suitably, the core-shell rubber particles have an average particle sizeof from about 50 μm to about 300 μm, such as from about 100 μm to about200 μm, for example from 100 μm to about 150 μm.

Desirably, the cyanoacrylate component comprises H₂C═C(CN)—COOR, whereinR is selected from alkyl, alkoxyalkyl, cycloalkyl, alkenyl, aralkyl,aryl, allyl and haloalkyl groups.

Optionally, the cationic catalyst comprises salts of lithium and metalsfrom Group II of the Periodic Table, and non-nucleophilic acids.

The cationic catalyst may be a non-nucleophilic acid having a pH of lessthan 1.0 when measured as a 10% by weight solution in water.

The cationic catalyst may be a member selected from the group consistingof fluoroboric, fluoroarsenic, fluoroantimonic and fluorophosphoricacids; lithium tetrafluoroborate, calcium di-tetrafluoroborate,magnesium di-tetrafluoroborate, lithum hexaflourophosphate, calciumdi-hexaflourophosphate, magnesium di-hexaflourophosphate, lithiumhexaflouroantimonate and lithium hexaflouroarsenate; lanthanide triflatesalts, aryl iodonium salts, aryl sulfonium salts, lanthanum triflate,ytterbium triflate, trimethoxyboroxine, trimethoxyboroxine-aluminumacetyl acetonate, amine-boron trihalide complexes, quaternary ammoniumsalts, quaternary phosphonium salts, tri-aryl sulfonium salts, di-aryliodonium salts, and diazonium salts; trialkoxyboroxine curing agents;and combinations thereof.

The cationic curable component may be selected from an epoxy component,an episulfide component, an oxetane component, a vinyl ether componentand combinations thereof.

Suitably, the cationic curable component is an epoxy component selectedfrom the group consisting of cycloaliphatic epoxy, aromatic epoxy,aliphatic epoxy and hydrogenated aromatic epoxy.

Desirably, the epoxy component comprises a member selected from thegroup consisting of epoxy-functionalized: bisphenol-A, bisphenol-F,bisphenol-E, bisphenol-S and biphenyl, and hydrogenated versions of suchepoxy functionalised species.

Suitably, the first part is housed in a first chamber of a dual chambersyringe and the second part is housed in a second chamber of the dualchamber syringe.

The first part may further comprise a stabiliser such as phosphoricacid.

The second part may further comprise at least one of a plasticizer, afiller and a toughener.

For example, the toughener may be a member selected from the groupconsisting of (1) (a) reaction products of the combination of ethylene,methyl acrylate and monomers having carboxylic acid cure sites, (2) (b)dipolymers of ethylene and methyl acrylate, (3) combinations of (a) and(b), (4) vinylidene chloride-acrylonitrile copolymers, (5) and vinylchloride/vinyl acetate copolymer, (6) copolymers of polyethylene andpolyvinyl acetate, and combinations thereof.

The first part and the second part may be present in a ratio of about1:1 by volume.

Optionally, the first part and the second part are each housed in aseparate chamber of a dual chambered container.

Advantageously, the compositions of the invention provide goodperformance across substrates constructed from a wide variety ofmaterials, for example metallic substrates and plastic substrates.

The composition is less prone to sag due to the presence of thepolyolefin fibres. In particular when the first part has an initialviscosity of from about viscosity of both the first part and the secondpart being of from at least about 6,000 mPa·s, to about 16,000 mPa·s.That is, the composition, which the first part and the second part has aviscosity of from at least about 6,000 mPa·s, to about 16,000 mPa·sprovides a composition which cures prior to deforming under thecompositions own weight once it is mixed with a second part as describedherein and applied as an adhesive.

Significantly the inclusion of the thixotropic agent in the first partof the composition to provide a the first part cyanoacrylate compositionwith an initial viscosity of from at least about 6,000 mPa·s to about16,000 mPa·s, and having a viscosity after ageing for 72 hours at 82° C.of from about 12,000 mPa·s to about 48,000 mPa·s does not adverselyaffect the fixture time or the toughness of the cured reaction product.

DETAILED DESCRIPTION

The invention will be more readily appreciated by a review of theexamples which follow.

Part A

The cyanoacrylate component includes cyanoacrylate monomers, such asthose represented by H₂C═C(CN)—COOR, where R is selected from C₁₋₁₅alkyl, C₂₋₁₅ alkoxyalkyl, C₃₋₁₅ cycloalkyl, C₂₋₁₅ alkenyl, C₇₋₁₅aralkyl, C₆₋₁₅ aryl, C₃₋₁₅ allyl and C₃₋₁₅ haloalkyl groups. Desirably,the cyanoacrylate monomer is selected from methyl cyanoacrylate,ethyl-2-cyanoacrylate, propyl cyanoacrylates, butyl cyanoacrylates (suchas n-butyl-2-cyanoacrylate), octyl cyanoacrylates, allyl cyanoacrylate,ß-methoxyethyl cyanoacrylate and combinations thereof. A particularlydesirable one is ethyl-2-cyanoacrylate (“ECA”).

The cyanoacrylate component should be included in the Part A compositionin an amount within the range of from about 50% to about 99.98% byweight, such as about 65% to about 85% by weight being desirable, andabout 75% to about 97% by weight of the total composition beingparticularly desirable.

As the cationic catalyst to be included in the Part A composition of thetwo-part adhesive system, a hard cation non-nucleophilic anion catalystshould be used. Examples of such catalysts include salts of lithium andmetals from Group II of the Periodic Table, and non-nucleophilic acids.Such non-nucleophilic acids have a pH of less than 1.0 when measured asa 10% by weight solution in water and the anion portion of such acidsdoes readily participate in displacement reactions with organic halides.Examples of the Group II metal salts include calcium and magnesium.Examples of non-nucleophilic acids include perchloric, fluoroboric,fluoroarsenic, fluoroantimonic and fluorophosphoric acids. Accordingly,examples of hard cation non-nucleophilic anion salts include lithiumtetrafluoroborate, calcium di-tetrafluoroborate, magnesiumdi-tetrafluoroborate, lithium hexaflourophosphate, calciumdi-hexaflourophosphate, magnesium di-hexaflourophosphate, lithiumhexaflouroantimonate and lithium hexaflouroarsenate.

The cationic catalyst may also include lanthanide triflate salts, aryliodonium salts, aryl sulfonium salts, lanthanum triflate, ytterbiumtriflate, trimethoxyboroxine, trimethoxyboroxine-aluminum acetylacetonate, amine-boron trihalide complexes, quaternary ammonium salts,quaternary phosphonium salts, tri-aryl sulfonium salts, di-aryl iodoniumsalts, and diazonium salts.

Another cationic catalyst suitable for use herein in the Part Acomposition of the adhesive system are trialkoxyboroxine curing agents,such as are described in U.S. Pat. Nos. 4,336,367 and 6,617,400, thedisclosures of each of which are hereby incorporated herein byreference. Of course, combinations of any two or more of these cationiccatalysts may be used as well.

Also suitable for use as some or all of the cationic catalyst are borontrifluoride, boron trifluoride-etherate, sulphur trioxide (andhydrolysis products thereof) and methane sulfonic acid, which areoftentimes used to stabilize cyanoacrylate monomers against anionicpolymerization (see below), a known issue in shelf life stabilization.

Typically, the amount of cationic catalyst will fall in the range ofabout 0.001 weight percent up to about 10.00 weight percent of thecomposition, desirably about 0.01 weight percent up to about 5.00 weightpercent of the composition, such as about 0.50 to 2.50 weight percent ofthe composition.

Additives may be included in the Part A composition of the adhesivesystem to confer physical properties, such as improved fixture speed,improved shelf-life stability, flexibility, thixotropy, increasedviscosity, colour, and improved toughness. Such additives therefore maybe selected from accelerators, free radical stabilizers, anionicstabilizers, gelling agents, thickeners, thixotropy conferring agents,dyes, toughening agents, plasticizers and combinations thereof.

These additives are discussed in more detail below. However, theaccelerators and stabilizers are discussed here.

One or more accelerators may also be used in the adhesive system,particularly, in the Part A composition, to accelerate cure of thecyanoacrylate component. Such accelerators may be selected fromcalixarenes and oxacalixarenes, silacrowns, crown ethers, cyclodextrins,poly(ethyleneglycol) di(meth)acrylates, ethoxylated hydric compounds andcombinations thereof.

Of the calixarenes and oxacalixarenes, many are known, and are reportedin the patent literature. See e.g. U.S. Pat. Nos. 4,556,700, 4,622,414,4,636,539, 4,695,615, 4,718,966, and 4,855,461, the disclosures of eachof which are hereby expressly incorporated herein by reference.

For instance, as regards calixarenes, those within the structure beloware useful herein:

where R¹ is alkyl, alkoxy, substituted alkyl or substituted alkoxy; R²is H or alkyl; and n is 4, 6 or 8.

One particularly desirable calixarene is tetrabutyltetra[2-ethoxy-2-oxoethoxy]calix-4-arene.

A host of crown ethers are known. For instance, examples which may beused herein either individually or in combination include 15-crown-5,18-crown-6, dibenzo-18-crown-6, benzo-15-crown-5-dibenzo-24-crown-8,dibenzo-30-crown-10, tribenzo-18-crown-6, asym-dibenzo-22-crown-6,dibenzo-14-crown-4, dicyclohexyl-18-crown-6, dicyclohexyl-24-crown-8,cyclohexyl-12-crown-4, 1,2-decalyl-15-crown-5, 1,2-naphtho-15-crown-5,3,4,5-naphtyl-16-crown-5, 1,2-methyl-benzo-18-crown-6,1,2-methylbenzo-5, 6-methylbenzo-18-crown-6, 1,2-t-butyl-18-crown-6,1,2-vinylbenzo-15-crown-5, 1,2-vinylbenzo-18-crown-6,1,2-t-butyl-cyclohexyl-18-crown-6, asym-dibenzo-22-crown-6 and1,2-benzo-1,4-benzo-5-oxygen-20-crown-7. See U.S. Pat. No. 4,837,260(Sato), the disclosure of which is hereby expressly incorporated here byreference.

Of the silacrowns, again many are known, and are reported in theliterature. For instance, a typical silacrown may be represented withinthe structure below:

where R³ and R⁴ are organo groups which do not themselves causepolymerization of the cyanoacrylate monomer, R⁵ is H or CH₃ and n is aninteger of between 1 and 4. Examples of suitable R³ and R⁴ groups are Rgroups, alkoxy groups, such as methoxy, and aryloxy groups, such asphenoxy. The R³ and R⁴ groups may contain halogen or other substituents,an example being trifluoropropyl. However, groups not suitable as R⁴ andR⁵ groups are basic groups, such as amino, substituted amino andalkylamino.

Specific examples of silacrown compounds useful in the inventivecompositions include:

dimethylsila-11-crown-4;

dimethylsila-14-crown-5;

and dimethylsila-17-crown-6. See e.g., U.S. Pat. No. 4,906,317 (Liu),the disclosure of which is hereby expressly incorporated herein byreference.

Many cyclodextrins may be used in connection with the present invention.For instance, those described and claimed in U.S. Pat. No. 5,312,864(Wenz), the disclosure of which is hereby expressly incorporated hereinby reference, as hydroxyl group derivatives of an α, β or γ-cyclodextrinwhich is at least partly soluble in the cyanoacrylate would beappropriate choices for use herein as an accelerator component.

In addition, poly(ethylene glycol) di(meth)acrylates suitable for useherein include those within the structure below:

where n is greater than 3, such as within the range of 3 to 12, with nbeing 9 as particularly desirable. More specific examples include PEG200 DMA, (where n is about 4) PEG 400 DMA (where n is about 9), PEG 600DMA (where n is about 14), and PEG 800 DMA (where n is about 19), wherethe number (e.g., 400) represents the average molecular weight of theglycol portion of the molecule, excluding the two methacrylate groups,expressed as grams/mole (i.e., 400 g/mol). A particularly desirable PEGDMA is PEG 400 DMA.

And of the ethoxylated hydric compounds (or ethoxylated fatty alcoholsthat may be employed), appropriate ones may be chosen from those withinthe structure below:

where C_(m) can be a linear or branched alkyl or alkenyl chain, m is aninteger between 1 to 30, such as from 5 to 20, n is an integer between 2to 30, such as from 5 to 15, and R may be H or alkyl, such as C₁₋₆alkyl.

Commercially available examples of such materials include those offeredunder the DEHYDOL tradename from Cognis Deutschland GmbH & Co. KGaA,Dusseldorf, Germany, such as DEHYDOL 100.

In addition, accelerators embraced within the structure below:

where R is hydrogen, C₁₋₆ alkyl, C₁₋₆ alkyloxy, alkyl thioethers,haloalkyl, carboxylic acid and esters thereof, sulfinic, sulfonic andsulfurous acids and esters, phosphinic, phosphonic and phosphorous acidsand esters thereof, Z is a polyether linkage, n is 1-12 and p is 1-3 areas defined above, and R′ is the same as R, and g is the same as n.

A particularly desirable chemical within this class as an acceleratorcomponent is:

where n and m combined are greater than or equal to 12.

The accelerator should be included in the composition in an amountwithin the range of from about 0.01% to about 10% by weight, with therange of about 0.1 to about 0.5% by weight being desirable, and about0.4% by weight of the total composition being particularly desirable.

Stabilizers useful in the Part A composition of the adhesive systeminclude free-radical stabilizers, anionic stabilizers and stabilizerpackages that include combinations thereof. The identity and amount ofsuch stabilizers are well known to those of ordinary skill in the art.See e.g. U.S. Pat. Nos. 5,530,037 and 6,607,632, the disclosures of eachof which are hereby incorporated herein by reference. Commonly usedfree-radical stabilizers include hydroquinone, while commonly usedanionic stabilizers include boron trifluoride, borontrifluoride-etherate, sulphur trioxide (and hydrolysis products thereof)and methane sulfonic acid. These anionic stabilizers can also serve asthe cationic catalyst or a portion thereof, as noted above.

Part B

Cationically curable monomers for use in the Part B composition of theadhesive system include epoxy monomers, episulfide monomers, oxetanemonomers, and combinations thereof.

Epoxy monomers for use in Part B of the composition of the adhesivesystem include a host of epoxy monomers, with some of the epoxy monomersbeing aromatic, while others are aliphatic and still others arecycloaliphatic. Examples of such epoxy monomers include bisphenol Fdiglycidyl ethers (and hydrogenated versions thereof), bisphenol Adiglycidyl ethers (and hydrogenated versions thereof), bisphenol Sdiglycidyl ethers (and hydrogenated versions thereof), bisphenol Ediglycidyl ethers (and hydrogenated versions thereof), biphenyldiglycidyl ethers (and hydrogenated versions thereof),4-vinyl-1-cyclohexene diepoxide, butanediol diglycidyl ether,neopentylglycol diglycidyl ether,3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, limonenediepoxide, hexanediol diglycidyl ether, trimethylolpropane triglycidylether, aniline diglycidyl ether, diglycidyl ether of propylene glycol,cyanuric acid triglycidyl ether, ortho-phthalic acid diglycidyl ether,diglycidyl ester of linoleic dimer acid, dicyclopentadiene diepoxide,tetrachlorobisphenol A glycidyl ethers,1,1,1-tris(p-hydroxyphenyl)ethane glycidyl ether, tetra glycidyl etherof tetrskis(4-hydroxyphenyl)ethane, epoxy phenol novolac resins, epoxycresol novolac resins, tetraglycidyl-4,4′-diaminodiphenylmethane, andthe like.

Among the commercially available epoxy resins suitable for use arepolyglycidyl derivatives of phenolic compounds, such as those availableunder the tradenames EPON 828, EPON 1001, EPON 1009, and EPON 1031, fromShell Chemical Co.; DER 331, DER 332, DER 334, and DER 542 from DowChemical Co.; GY285 from Ciba Specialty Chemicals, Tarrytown, N.Y.; andBREN-S from Nippon Kayaku, Japan; epoxidized polybutadienes, such asthose sold under the trade designation PolyBD from Sartomer, EPOLEAD PB3600 from Daicel, JP-100 and JP-200 from Nippon Soda, epoxidised liquidisoprene rubbers such as KL-610, KL-613 and KL-630T from Kuraray; andepoxidised liquid polyisoprenes such as EPDXYPRENE 25 and EPDXYPRENE 50from Sanyo Corporation. Other suitable epoxy resins include polyepoxidesprepared from polyols and the like and polyglycidyl derivatives ofphenol-formaldehyde novolacs, the latter of which are availablecommercially under the tradenames DEN 431, DEN 438, and DEN 439 from DowChemical Company. Cresol analogs are also available commercially ECN1235, ECN 1273, and ECN 1299 from Ciba Specialty Chemicals. SU-8 is abisphenol A-type epoxy novolac available from Resolution. Of course,cycloaliphatic epoxy resins, such as those available under the CYRACUREtradename, and hydrogenated bisphenol and biphenyl type epoxy resins, asnoted, such as those available under the EPALLOY tradename, are suitablefor use herein.

Cycloaliphatic epoxy resins contain at least one cycloaliphatic groupand at least one oxirane group, oftentimes two oxirane groups.Representative cycloaliphatic epoxy resins include2-(3,4-epoxy)cyclohexyl-5,5-spiro-(3,4-epoxy)cyclohexane-m-dioxane,3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate,vinyl cyclohexanedioxide, bis(3,4-epoxycyclohexylmethyl)adipate,bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, exo-exobis(2,3-epoxycyclopentyl) ether, endo-exo bis(2,3-epoxycyclopentyl)ether, 2,2-bis(4-(2,3-epoxypropoxy)cyclohexyl)propane,2,6-bis(2,3-epoxypropoxycyclohexyl-p-dioxane),2,6-bis(2,3-epoxypropoxy)norbornene, the diglycidylether of linoleicacid dimer, limonene dioxide, a-pinene oxide, 3-vinylcyclohexene oxide,3-vinylcyclohexene dioxide, epoxidisedpoly(1,3-butadiene-acrylonitrile), epoxidised soybean oil, epoxidisedcastor oil, epoxidised linseed oil, 2,2-bis(3,4-epoxycyclohexyl)propane,dicyclopentadiene dioxide, tricyclopentadiene dioxide,tetracyclopentadiene dioxide,1,2-epoxy-6-(2,3-epoxypropoxy)hexahydro-4,7-methanoindane,p-(2,3-epoxy)cyclopentylphenyl-2,3-epoxypropylether,1-(2,3-epoxypropoxy)phenyl-5,6-epoxyhexahydro-4,7-methanoindane,o-(2,3epoxy)cyclopentylphenyl-2,3-epoxypropyl ether),1,2-bis[5-(1,2-epoxy)-4,7-hexahydromethanoindanoxyl]ethane,cyclopentenylphenyl glycidyl ether, cyclohexanediol diglycidyl ether,and diglycidyl hexahydrophthalate. Siloxane functional epoxy resins mayalso be utilised such as1,3-bis(3,4-epoxycyclohexyl-2-ethyl)-1,1,3,3-tetramethyldisiloxane andother epoxy functional linear/cyclic siloxanes such as those disclosedin U.S. Pat. No. 7,777,064, the disclosure of which being herebyexpressly incorporated herein by reference. In particular embodimentscycloaliphatic epoxy resins are3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate and3,4-epox-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate.Other examples of cycloaliphatic epoxies suitable for use herein includethose disclosed and described in U.S. Pat. No. 6,429,281 (Dershem), thedisclosure of which being hereby expressly incorporated herein byreference.

And combinations of the epoxy resins are also desirable for use herein.

The episulfide monomer may simply be the full or partialsulphur-containing three-membered ring version of the base epoxymonomer.

The oxetane monomers may be chosen from:

The vinyl ether monomer may be selected from a host of materials, suchas those commercially available under the tradename VEctomer fromVertellus Performance Materials Inc., Greensboro, N.C. Examples includeVEctomer vinyl ether 4010 [Bis-(4-vinyl oxy butyl) isophthalate],VEctomer vinyl ether 4060 [Bis(4-vinyl oxy butyl) adipate], and VEctomervinyl ether 5015 [Tris(4-vinyloxybutyl)trimellitate].

The epoxy, episulfide, oxetane and/or vinyl ether monomer may be onethat is functionalized with one or more alkoxy silane groups. Examplesof such materials include those commercially available from Gelest Inc.,Morrisville, Pa.

As discussed above, additives may be included in either or both of thePart A or the Part B compositions to influence a variety of performanceproperties.

Fillers contemplated for optional use include, for example, aluminiumnitride, boron nitride, silicon carbide, diamond, graphite, berylliumoxide, magnesia, silicas, such as fumed silica or fused silica, alumina,perfluorinated hydrocarbon polymers (i.e., TEFLON), thermoplasticpolymers, thermoplastic elastomers, mica, glass powder and the like.Preferably, the particle size of these fillers will be about 20 micronsor less.

As regards silicas, the silica may have a mean particle diameter on thenanoparticle size; that is, having a mean particle diameter on the orderof 10⁻⁹ meters. The silica nanoparticles can be pre-dispersed in epoxyresins, and may be selected from those available under the tradenameNANOPDX, from Nanoresins, Germany. NANOPDX is a tradename for a productfamily of silica nanoparticle reinforced epoxy resins showing anoutstanding combination of material properties. The silica phaseconsists of surface-modified, synthetic SiO₂ nanospheres with less than50 nm diameter and an extremely narrow particle size distribution. TheSiO₂ nanospheres are agglomerate-free dispersions in the epoxy resinmatrix resulting in a low viscosity for resins containing up to 50 wt %silica.

A commercially available example of the NANOPDX products particularlydesirable for use herein includes NANOPDX A610 (a 40 percent by weightdispersion in a cycloaliphatic epoxy resin matrix). The NANOPDX productsare believed to have a particle size of about 5 nm to about 80 nm,though the manufacturer reports less than 50 nm.

The silica component should be present in an amount in the range ofabout 0.1 to about 20 percent by weight, such as about 1 to about 10percent by weight, desirably about 2 to about 4 percent by weight, basedon the total weight of the composition. For example, the silicacomponent may be present in an amount of from about 2 to about 5 weightpercent in the Part B component, based on the total weight of the Part Bcomposition. Preferably, the silica component is in Part B only.

Flexibilizers (also called plasticizers) contemplated for use in thecompositions described herein include branched polyalkanes orpolysiloxanes that can lower the T_(g) of the composition. Suchflexibilizers include, for example, polyethers, polyesters, polythiols,polysulfides, and the like. If used, flexibilizers typically are presentin the range of about 0.5 weight percent up to about 30 weight percentof the composition.

The flexibilizers may also be reactive; that is, they may befunctionalized so as to react into the cured reaction product. In suchcases, hydroxyl-functionalized resins can be used, as they tend toco-react with cationically curable components, such as epoxy resins, andthus used can modify the mechanical properties of the cured products.

For instance, hydroxy-functionalized aliphatic polyester diols provideimproved flexibility to the cured composition. One commerciallyavailable example of the diol is K-FLEX A307, which is from KingIndustries. K-FLEX A307 is reported by the manufacturer to be a lowviscosity, 100% solids linear, saturated, aliphatic polyester diol withprimary hydroxyl groups. K-FLEX A307 is promoted to have been designedas a flexibility modifier for acrylic/isocyanates and acrylic/melaminesystems. Commercial applications are advertised as automotive OEM,automotive refinish, aerospace, industrial maintenance, and plasticcoatings.

Others include PolyTHF 650/1400/2000/2900 (sold under the trade nameTERATHANE), polycaprolactone diols and triols (Aldrich),polydimethylsiloxane-polycaprolactone diols (such as WAX 350 OH D fromWacker), K-PURE CDR-3441, CDR-3319 (King Industry), primary or secondaryhydroxyl terminated polybutadienes/hydrogenated polybutadienes (CrayValley, such as PolyBd/Krasol materials), and hydrogenated castor oils,such as THIXCIN R, THIXCIN E (Elementis Specialties), and the POLYCINseries (Vertellus Specialties Inc.).

Tougheners contemplated for use particularly in the Part A compositioninclude elastomeric polymers selected from elastomeric copolymers of alower alkene monomer and (i) acrylic acid esters, (ii) methacrylic acidesters or (iii) vinyl acetate, such as acrylic rubbers; polyesterurethanes; ethylene-vinyl acetates; fluorinated rubbers;isoprene-acrylonitrile polymers; chlorosulfinated polyethylenes; andhomopolymers of polyvinyl acetate were found to be particularly useful.[See U.S. Pat. No. 4,440,910 (O'Connor), the disclosure of which ishereby expressly incorporated herein by reference]. The elastomericpolymers are described in the '910 patent as either homopolymers ofalkyl esters of acrylic acid; copolymers of another polymerizablemonomer, such as lower alkenes, with an alkyl or alkoxy ester of acrylicacid; and copolymers of alkyl or alkoxy esters of acrylic acid. Otherunsaturated monomers which may be copolymerized with the alkyl andalkoxy esters of acrylic include dienes, reactive halogen-containingunsaturated compounds and other acrylic monomers such as acrylamides.

For instance, one group of such elastomeric polymers are copolymers ofmethyl acrylate and ethylene, manufactured by DuPont, under the name ofVAMAC, such as VAMAC N123 and VAMAC B-124. VAMAC N123 and VAMAC B-124are reported by DuPont to be a master batch of ethylene/acrylicelastomer. The DuPont material VAMAC G is a similar copolymer, butcontains no fillers to provide colour or stabilizers. VAMAC VCS rubberappears to be the base rubber, from which the remaining members of theVAMAC product line are compounded. VAMAC VCS (also known as VAMAC MR) isa reaction product of the combination of ethylene, methyl acrylate andmonomers having carboxylic acid cure sites, which once formed is thensubstantially free of processing aids such as the release agentsoctadecyl amine, complex organic phosphate esters and/or stearic acid,and anti-oxidants, such as substituted diphenyl amine.

Recently, DuPont has provided to the market under the trade designationVAMAC VMX 1012 and VCD 6200, which are rubbers made from ethylene andmethyl acrylate. It is believed that the VAMAC VMX 1012 rubber possesseslittle to no carboxylic acid in the polymer backbone. Like the VAMAC VCSrubber, the VAMAC VMX 1012 and VCD 6200 rubbers are substantially freeof processing aids such as the release agents octadecyl amine, complexorganic phosphate esters and/or stearic acid, and anti-oxidants, such assubstituted diphenyl amine, noted above. All of these VAMAC elastomericpolymers are useful herein.

In addition, vinylidene chloride-acrylonitrile copolymers [see U.S. Pat.No. 4,102,945 (Gleave)] and vinyl chloride/vinyl acetate copolymers [seeU.S. Pat. No. 4,444,933 (Columbus)] may be included in the Part Acomposition. Of course, the disclosures of each these U.S. patents arehereby incorporated herein by reference in their entirety.

Copolymers of polyethylene and polyvinyl acetate, available commerciallyunder the tradename LEVAMELT by LANXESS Limited, are useful.

A range of LEVAM ELT agents is available and includes for example,LEVAMELT 400, LEVAMELT 600 and LEVAMELT 900. The LEVAMELT productsdiffer in the amount of vinyl acetate present. For example, LEVAMELT 400comprises an ethylene-vinyl acetate copolymer comprising 40 wt % vinylacetate. The LEVAMELT-brand products are supplied in granular form. Thegranules are almost colourless and dusted with silica and talc. TheLEVAMELT-brand products consist of methylene units forming a saturatedmain chain with pendant acetate groups. The presence of a fullysaturated main chain is an indication that LEVAMELT is a particularlystable polymer. It does not contain any reactive double bonds which makeconventional rubbers prone to aging reactions, ozone and UV light. Thesaturated backbone is reported to make it robust.

Interestingly, depending on the ratio of polyethylene/polyvinylacetate,the solubilities of these LEVAMELT elastomers change in differentmonomers and also the ability to toughen changes as a result of thesolubility.

The LEVAMELT elastomers are available in pellet form and are easier toformulate than other known elastomeric toughening agents.

VINNOL brand surface coating resins available commercially from WackerChemie AG, Munich, Germany represent a broad range of vinylchloride-derived copolymers and terpolymers that are promoted for use indifferent industrial applications. The main constituents of thesepolymers are different compositions of vinyl chloride and vinyl acetate.The terpolymers of the VINNOL product line additionally contain carboxylor hydroxyl groups. These vinyl chloride/vinyl acetate copolymers andterpolymers may also be used.

VINNOL surface coating resins with carboxyl groups are terpolymers ofvinyl chloride, vinyl acetate and dicarboxylic acids, varying in termsof their molar composition and degree and process of polymerization.These terpolymers are reported to show excellent adhesion, particularlyon metallic substrates.

VINNOL surface coating resins with hydroxyl groups are copolymers andterpolymers of vinyl chloride, hydroxyacrylate and dicarboxylate,varying in terms of their composition and degree of polymerization.

VINNOL surface coating resins without functional groups are copolymersof vinyl chloride and vinyl acetate of variable molar composition anddegree of polymerization.

Rubber particles, especially rubber particles that have relatively smallaverage particle size (e.g., less than about 500 nm or less than about200 nm), may also be included, particularly in the Part B composition.The rubber particles may or may not have a shell common to knowncore-shell structures.

In the case of rubber particles having a core-shell structure, suchparticles generally have a core comprised of a polymeric material havingelastomeric or rubbery properties (i.e., a glass transition temperatureless than about 0° C., e.g., less than about −30° C.) surrounded by ashell comprised of a non-elastomeric polymeric material (i.e., athermoplastic or thermoset/crosslinked polymer having a glass transitiontemperature greater than ambient temperatures, e.g., greater than about50° C.). For example, the core may be comprised of a diene homopolymeror copolymer (for example, a homopolymer of butadiene or isoprene, acopolymer of butadiene or isoprene with one or more ethylenicallyunsaturated monomers such as vinyl aromatic monomers,(meth)acrylonitrile, (meth)acrylates, or the like) while the shell maybe comprised of a polymer or copolymer of one or more monomers such as(meth)acrylates (e.g., methyl methacrylate), vinyl aromatic monomers(e.g., styrene), vinyl cyanides (e.g., acrylonitrile), unsaturated acidsand anhydrides (e.g., acrylic acid), (meth)acrylamides, and the likehaving a suitably high glass transition temperature. Other rubberypolymers may also be suitably be used for the core, includingpolybutylacrylate or polysiloxane elastomer (e.g., polydimethylsiloxane,particularly crosslinked polydimethylsiloxane).

The rubber particle may be comprised of more than two layers (e.g., acentral core of one rubbery material may be surrounded by a second coreof a different rubbery material or the rubbery core may be surrounded bytwo shells of different composition or the rubber particle may have thestructure soft core, hard shell, soft shell, hard shell). In oneembodiment of the invention, the rubber particles used are comprised ofa core and at least two concentric shells having different chemicalcompositions and/or properties. Either the core or the shell or both thecore and the shell may be crosslinked (e.g., ionically or covalently).The shell may be grafted onto the core. The polymer comprising the shellmay bear one or more different types of functional groups (e.g., epoxygroups) that are capable of interacting with other components of thecompositions of the present invention.

Typically, the core will comprise from about 50 to about 95 weightpercent of the rubber particles while the shell will comprise from about5 to about 50 weight percent of the rubber particles.

Methods of preparing rubber particles having a core-shell structure arewell-known in the art and are described, for example, in U.S. Pat. Nos.4,419,496, 4,778,851, 5,981,659, 6,111,015, 6,147,142 and 6,180,693,each of which being incorporated herein by reference in its entirety.

Rubber particles having a core-shell structure may be prepared as amasterbatch where the rubber particles are dispersed in one or moreepoxy resins such as a diglycidyl ether of bisphenol A. For example, therubber particles typically are prepared as aqueous dispersions oremulsions. Such dispersions or emulsions may be combined with thedesired epoxy resin or mixture of epoxy resins and the water and othervolatile substances removed by distillation or the like. One method ofpreparing such masterbatches is described in more detail inInternational Patent Publication No. WO 2004/108825, the disclosure ofwhich being expressly incorporated herein by reference in its entirety.For example, an aqueous latex of rubber particles may be brought intocontact with an organic medium having partial solubility in water andthen with another organic medium having lower partial solubility inwater than the first organic medium to separate the water and to providea dispersion of the rubber particles in the second organic medium. Thisdispersion may then be mixed with the desired epoxy resin(s) andvolatile substances removed by distillation or the like to provide themasterbatch.

Particularly suitable dispersions of rubber particles having acore-shell structure in an epoxy resin matrix are available from KanekaCorporation.

For instance, the core may be formed predominantly from feed stocks ofpolybutadiene, polyacrylate, polybutadiene/acrylonitrile mixture,polyols and/or polysiloxanes or any other monomers that give a low glasstransition temperature. The outer shells may be formed predominantlyfrom feed stocks of polymethylmethacrylate, polystyrene or polyvinylchloride or any other monomers that give a higher glass transitiontemperature.

Core-shell rubber particles made in this way may be dispersed in athermosetting resin matrix, such as an epoxy matrix or a phenolicmatrix. Examples of epoxy matrices include the diglycidyl ethers ofbisphenol A, F or S, or biphenol, novalac epoxies, and cycloaliphaticepoxies. Examples of phenolic resins include bisphenol-A basedphenoxies. The matrix material ordinarily is liquid at room temperature.

When used, these core-shell rubber particles allow for toughening tooccur in the composition and oftentimes in a predictable manner—in termsof temperature neutrality toward cure—because of the substantial uniformdispersion, which is ordinarily observed in the core-shell rubberparticles as they are offered for sale commercially.

Many of the core-shell rubber particle structures available from Kaneka,such as those available under the KANEACE tradename, are believed tohave a core made from a copolymer of (meth)acrylate-butadiene-styrene,where the butadiene is the primary component in the phase separatedparticles, dispersed in epoxy resins. Other commercially availablemasterbatches of core-shell rubber particles dispersed in epoxy resinsinclude GENIOPERL M23A (a dispersion of 30 weight percent core-shellparticles in an aromatic epoxy resin based on bisphenol A diglycidylether; the core-shell particles have an average diameter of ca. 100 nmand contain a crosslinked silicone elastomer core onto which anepoxy-functional acrylate copolymer has been grafted); the siliconeelastomer core represents about 65 weight percent of the core-shellparticle), available from Wacker Chemie GmbH.

In the case of those rubber particles that do not have such a shell, therubber particles may be based on the core of such structures.

Preferably, the rubber particles are relatively small in size. Forexample, the average particle size may be from about 50 to about 300 μm,or from about 100 to about 200 μm.

The rubber particles generally are comprised of a polymeric materialhaving elastomeric or rubbery properties (i.e., a glass transitiontemperature less than about 0° C., e.g., less than about −30° C.). Forexample, the rubber particles may be comprised of a diene homopolymer orcopolymer (for example, a homopolymer of butadiene or isoprene, acopolymer of butadiene or isoprene with one or more ethylenicallyunsaturated monomers such as vinyl aromatic monomers,(meth)acrylonitrile, (meth)acrylates, or the like) and polysiloxanes.The rubber particles may contain functional groups such as carboxylategroups, hydroxyl groups or the like and may have a linear, branched,crosslinked, random copolymer or block copolymer structure.

For instance, the rubber particles may be formed predominantly from feedstocks of dienes such as butadiene, (meth)acrylates, ethylenicallyunsaturated nitriles such as acrylonitrile, and/or any other monomersthat when polymerized or copolymerized yield a polymer or copolymerhaving a low glass transition temperature.

The rubber particles may be used in a dry form or may be dispersed in amatrix, as noted above.

Typically, the composition may contain from about 0.05 to about 35weight percent (in one embodiment, from about 15 to about 30 weightpercent) rubber particles.

Suitably, when present in Part A, core-shell rubber particles arepresent in an amount of from about 0.1 to about 7.5 weight percent,based on the total weight of the composition of Part A. Optionally,core-shell rubber particles are present in Part A in an amount of fromabout 1 to about 5 weight percent, based on the total weight of thecomposition of Part A.

Combinations of different rubber particles may advantageously be used inthe present invention. The rubber particles may differ, for example, inparticle size, the glass transition temperatures of their respectivematerials, whether, to what extent and by what the materials arefunctionalized, and whether and how their surfaces are treated.

A portion of the rubber particles may be supplied in the form of amasterbatch where the particles are stably dispersed in an epoxy resinmatrix and another portion may be supplied to the adhesive compositionin the form of a dry powder (i.e., without any epoxy resin or othermatrix material). For example, the adhesive composition may be preparedusing both a first type of rubber particles in dry powder form having anaverage particle diameter of from about 0.1 to about 0.5 μm and a secondtype of rubber particles stably dispersed in a matrix of liquidbisphenol A diglycidyl ether at a concentration of from about 5 to about50 percent by weight having an average particle diameter of from about25 to about 200 nm. The weight ratio of first type:second type rubberparticles may be from about 1.5:1 to about 0.3:1, for example.

The chemical composition of the rubber particles may be essentiallyuniform throughout each particle. However, the outer surface of theparticle may be modified by reaction with a coupling agent, oxidizingagent or the like so as to enhance the ability to disperse the rubberparticles in the adhesive composition (e.g., reduce agglomeration of therubber particles, reduce the tendency of the rubber particles to settleout of the adhesive composition). Modification of the rubber particlesurface may also enhance the adhesion of the epoxy resin matrix to therubber particles when the adhesive is cured. The rubber particles mayalternatively be irradiated so as to change the extent of crosslinkingof the polymer(s) constituting the rubber particles in different regionsof the particle. For example, the rubber particles may be treated withgamma radiation such that the rubber is more highly crosslinked near thesurface of the particle than in the centre of the particle.

Rubber particles that are suitable for use in the present invention areavailable from commercial sources. For example, rubber particlessupplied by Eliokem, Inc. may be used, such as NEP R0401 and NEP R401S(both based on acrylonitrile/butadiene copolymer); NEP R0501 (based oncarboxylated acrylonitrile/butadiene copolymer; CAS No. 9010-81-5); NEPR0601A (based on hydroxy-terminated polydimethylsiloxane; CAS No.70131-67-8); and NEP R0701 and NEP 0701S (based onbutadiene/styrene/2-vinylpyridine copolymer; CAS No. 25053-48-9). Alsothose available under the PARALOID tradename, such as PARALOID 2314,PARALOID 2300, and PARALOID 2600, from Dow Chemical Co., Philadelphia,Pa., and those available under the STAPHYLOID tradename, such asSTAPHYLOID AC-3832, from Ganz Chemical Co., Ltd., Osaka, Japan.

Rubber particles that have been treated with a reactive gas or otherreagent to modify the outer surfaces of the particles by, for instance,creating polar groups (e.g., hydroxyl groups, carboxylic acid groups) onthe particle surface, are also suitable for use in the presentinvention. Illustrative reactive gases include, for example, ozone, Cl₂,F₂, O₂, SO₃, and oxidative gases. Methods of surface modifying rubberparticles using such reagents are known in the art and are described,for example, in U.S. Pat. Nos. 5,382,635; 5,506,283; 5,693,714; and5,969,053, each of which is incorporated herein by reference in itsentirety. Suitable surface modified rubber particles are also availablefrom commercial sources, such as the rubbers sold under the tradenameVISTAMER by Exousia Corporation.

Where the rubber particles are initially provided in dry form, it may beadvantageous to ensure that such particles are well dispersed in theadhesive composition prior to curing the adhesive composition. That is,agglomerates of the rubber particles are preferably broken up so as toprovide discrete individual rubber particles, which may be accomplishedby intimate and thorough mixing of the dry rubber particles with othercomponents of the adhesive composition. For example, dry rubberparticles may be blended with epoxy resin and milled or melt compoundedfor a length of time effective to essentially completely disperse therubber particles and break up any agglomerations of the rubberparticles.

In addition, Nanoresins offers commercially products under thetradenames ALBIDUR (epoxy resins containing core-shell silicone rubberparticles; such as EP 2240, EP2240A, EP 5340);

ALBIFLEX (epoxy-siloxane block copolymer resins); and ALBI PDX (epoxyresins containing epoxy-nitrile butadiene rubber adducts).

Thickeners or viscosity modifiers are also useful. Useful materials inthis regard include polyvinyl butyral resins sold under the tradenameMOWITAL (Kuraray Ltd) such as Mowital B30T, B60T, B20H, B30H, B45H,B60H, B30HH and B60HH.

Other additives may also be included in the Part A composition. Forinstance, phosphoric acid may be included in the Part A composition.When included at levels in the range of about 50 ppm to about 1,000 ppm,such as about 100 to about 500 ppm, and applied to at least onealuminium substrate to be joined in a bonded assembly, improved strengthand strength retention may be observed. More specifically, humidity,heat aging and solvent immersion testing show that the addition ofphosphoric acid to the inventive two-part cyanoacrylate/cationicallycurable adhesive systems, may lead to dramatic improvements adhesivewith excellent properties on both metals and plastics, particularly onaluminium durability.

In practice, each of the Part A and the Part B compositions are housedin separate containment vessels in a device prior to use, where in usethe two-parts are expressed from the vessels mixed and applied onto asubstrate surface. The vessels may be chambers of a dual chamberedcartridge, where the separate parts are advanced through the chamberswith plungers through an orifice (which may be a common one or adjacentones) and then through a mixing dispense nozzle. Or the vessels may becoaxial or side-by-side pouches, which may be cut or torn and thecontents thereof mixed and applied onto a substrate surface.

The invention will be more readily appreciated by a review of theexamples, which follow.

Examples

Thixotropic agents were screened for compatibility with the first partof the composition which comprises a cyanoacrylate and a cationiccatalyst.

The compositions of Table 1 were prepared and the viscosity of eachcomposition was measured using a Brookfield CAP 2000 viscometer at 25°C., with spindle no. 5, and at 20 rpm. The initial appearance of thecompositions was also noted.

TABLE 1 Example Number 1 2 3 Amt Amt Amt Component (wt %) (wt %) (wt %)Ethyl-2-cyanoacrylate 77.19 76.79 76.41 BF₃ stock solution 0.99 0.990.98 Phosphoric acid 0.05 0.05 0.05 Cationic catalyst 0.97 0.97 0.96Thickener 19.8 19.70 19.6 Short Stuff E 380 F 1 1.5 2

The compositions of Table 1 were packed into 50 g 1:1 cartridge and agedfor 72 hours at 82° C. The viscosity of each composition was measuredafter 72 hours using Brookfield CAP 2000 (25° C., Spindle no. 5, 20rpm). The appearance and viscosity for each formulation was recordedbefore and after ageing, see Table 2.

TABLE 2 Example Number Properties 1 2 3 Initial Appearance White WhiteWhite Post 72 hrs at 82 C. Light Light Light Appearance yellow YellowYellow Initial Viscosity 7500 10350 11625 (mPa · s) Post 72 hrs at 82C., 12225 25500 23925 Viscosity (mPa · s) Post 1 week at 55 C., 945014050 15500 Viscosity (mPa · s) Post 2 week at 55 C., 12490 17250 18225Viscosity (mPa · s) Post 3 week at 55 C., 15825 22925 — Viscosity (mPa ·s)

The polyethylene fibres demonstrated an excellent thixotropic effect,increasing the viscosity of the Part A composition, without leading togelation of the samples. This represents a marked improvement overalternative thixotropic additives (when added to Part A), such asGENIOPERL P-52, BLENDEX 338 and KANE ACE B-564, each of which led tosample gelation of the cyanoacrylate component.

The properties of cured two-part curable compositions having thecompositions of Table 1 as the Part A component and having thecomposition provided in Table 3 as the Part B component were thenevaluated.

TABLE 3 Example Number/Amt (wt %) Component 4 Epoxy monomer 80.7 Fumedsilica 4 2,2′dipyridyl disulphide 0.3

Each of the Part A compositions in Table 1 was mixed together with thePart B composition of Table 3 and properties of the resulting curedcompositions were assessed.

TABLE 4 Adhesive Combination C1 C2 C3 Part A 1 1 2 2 3 3 (ExampleNumber) Part B 4 4 4 4 4 4 (Example Number) Aging conditions — 82° C./ —82° C./ 82° C./ 72 hrs 72 hrs 72 hrs Property Bead test (min) 5 4 5 4 45 0 mm gap 180 240 180 210 170 270 fixture time (s), Al substrate 1 mmgap 7 7 7 7 5 7 fixture time (min), Al substrate shear strength 19.8315.3 19.15 15.51 19.36 16.78 GBMS (after curing for 24 hours at 40° C.)(N/mm²) shear strength 13.82 9.85 13.33 10.16 13.2 13.11 Al (aftercuring for 24 hours at 40° C.) (N/mm²)

The bead test is carried out by depositing 3 beads of mixed adhesivehaving a length of 300 mm and a width of 4 mm on a polyethylene sheet.On completion of deposition of the third bead timing is begun. After 1minute an applicator stick is dragged across the third bead 120 mm fromthe start of the third bead. An applicator stick is then dragged acrossthe third bead a further 10 mm along the bead (i.e. 130 mm from thestart of the bead), and the process is repeated at 1 minute timeintervals and 10 mm length. There are three possible outcomes: (i) thebead is completely broken by dragging the applicator stick across thebead, and therefore the bead is deemed uncured; this time is marked withan “X”, and the time corresponding to the last “X” is recorded as theonset time; (ii) there is some resistance when dragging the applicatorstick across the bead and only some material is dragged from the bead,this means the bead is partially cured; this time point is marked with a“˜”; (iii) no residue is dragged away from the bead and a clicking noisecan be heard as the applicator stick is dragged across the bead; thistime point is marked with a “✓”, the time corresponding to the “✓” isrecorded as the cured time.

The fixture times were evaluated for each of the 2K compositions formedfrom Part A compositions of Table 1 combined with a Part B compositionas specified in Table 3 on lap shear adherend substrates constructedfrom Aluminium (Al). Fixture times were evaluated with a gap of 0 mmbetween the substrates and also with a gap of 1 mm between thesubstrates. Sufficient quantities of each part of the adhesivecomposition were applied to the lap substrates to ensure completecoverage of a 322.6 mm² (0.5 in.²) area. Fixture time which is definedas the minimum time required for bonded substrates to fully support asuspended 3 kg mass from one substrate whilst the other is clampedvertically was evaluated for adhesive combinations C1 to C3 as specifiedin Table 4.

The curable 2K compositions of the invention were applied as a coatingto a first lap shear adherend (for example a metallic substrate) and anassembly is prepared by clamping the first lap shear to the second lapshear with the curable 2K composition sandwiched between said first andsecond adherends. The clamped assembly is allowed to cure for a periodof 24 hours at 40° C., and lap shear strength was determined on anInstron, according to ASTM D1002-05.

The effect of including core-shell rubber particles in the compositionsof the invention was then assessed.

TABLE 5 Example Number 5 6 7 8 Amt Amt Amt Amt Component (wt %) (wt %)(wt %) (wt %) Ethyl-2-cyanoacrylate 75.628 74.07 72.51 74.848 BF₃ Stocksolution 0.97 0.95 0.93 0.96 stabiliser 0.052 0.05 0.05 0.052 Cationiccatalyst 0.95 0.93 0.91 0.94 Plasticiser 19.4 19 18.6 19.2 Blendex 338 00 0 3 Kane Ace M-521 2 3 5 0 Short Stuff E 380 F 1 2 2 1

Compositions as provided in Table 5 were prepared and the initial andaged viscosities of said compositions were evaluated. The compositionsof table 5 were packed into 50 g 1:1 cartridge and aged for 72 hours at82° C. The viscosity of each composition was measured after 72 hoursusing Brookfield CAP 2000 (25° C., Spindle no. 5, 20 rpm). Theappearance and viscosity for each formulation was recorded before andafter ageing, see Table 6.

TABLE 6 Example Number Properties 5 6 7 8 Initial Appearance White WhiteWhite White Post 72 hrs at Light Light Light Light 82° C. Appearanceyellow Yellow Yellow Yellow Initial Viscosity 9850 14625 15650 11550(mPa · s) Post 72 hrs at 18600 28800 35100 25800 82° C., Viscosity (mPa· s) Post 1 week at 13800 — — 16820 55° C., Viscosity (mPa · s) Post 2week at 15150 — — 20300 55° C., Viscosity (mPa · s) Post 3 week at 18825— — — 55° C., Viscosity (mPa · s)

The Part A compositions of Example 33A and 33D specified in Table 5 weremixed together with the Part B composition of Table 3 and properties ofthe resulting cured compositions were assessed, see table 7.

TABLE 7 Adhesive Combination C4 C5 Part A (Example 5 5 8 8 number) PartB (Example 4 4 4 4 number) Ageing conditions — 82° C./72 hrs — 82° C./72hrs Property Bead test (min) 5 4 5 5 0 mm gap 180 240 170 270 Fixturetime (s), Al substrate 1 mm gap 7 6 6 7 fixture time (min) Al substrateshear strength 19.88 16.19 16 16.78 GBMS (after curing for 24 hours at40° C.) (N/mm²) shear strength 13.34 11.17 13.36 10.67 Al (after curingfor 24 hours at 40° C.) (N/mm²)

The bead test, fixture times and shear strengths were determined asdescribed above.

Advantageously, the fixture time for the compositions of the inventionwere not deleteriously affected by the incorporation of the thixotropicagents in Part A of the 2K composition. Furthermore, lap shear strengthfor the cured compositions on grit blasted mild steal and on aluminiumsubstrates were comparable to those for prior art 2K compositions,despite the incorporation of the thixotropic agents in Part A of the 2Kcomposition. Advantageously, by incorporating the polyolefin fibres as athixotropic agent in the Part A composition, the viscosities of the PartA and Part B compositions are well matched and excellent mixing of saidparts is achieved.

The words “comprises/comprising” and the words “having/including” whenused herein with reference to the present invention are used to specifythe presence of stated features, integers, steps or components but donot preclude the presence or addition of one or more other features,integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination.

1. A two-part curable composition comprising: a. a first part comprisinga cyanoacrylate component, a cationic catalyst, and a plurality ofpolyolefin fibres; b. a second part comprising a cationic curablecomponent, and an initiator component; wherein when mixed together thecationic catalyst initiates cure of the cationic curable component. 2.The composition of claim 1, wherein the first part has an initialviscosity from about 6,000 to about 16,000 mPa·s, when measured at 25°C.; and wherein the first part has a viscosity of from about 12,000mPa·s to about 48,000 m·Pas, when measured at 25° C., after aging for 72hours at 82° C.
 3. The composition of claim 1, wherein the polyolefinfibres are high density polyethylene.
 4. The composition of claim 1,wherein the polymeric fibres have an average length of from about 400 μmto about 1000 μm.
 5. The composition of claim 1, wherein the polymericfibres have and average diameter of more than about 5 μm and less thanabout 25 μm.
 6. The composition of claim 1, wherein the polymeric fibresare present in an amount of from about 0.1 wt % to about 5 wt % based onthe total weight of the first part of the composition, such as in anamount of form about 0.5 wt % to about 3.5 wt % based on the totalweight of the first part of the composition.
 7. The composition of claim1, wherein the viscosity of the first part when measured at 25° C.,after ageing for 72 hours at 82° C., is less than about three times theinitial viscosity of the first part when measured at 25° C.
 8. Thecomposition of claim 1, further comprising core-shell rubber particlescomprising acrylonitrile butadiene-styrene copolymer and/or methylmethacrylate butadiene styrene copolymer.
 9. The composition of claim 8,wherein the core-shell rubber particles are present in an amount of fromabout 0.1 to about 5 weight percent, in the first part of thecomposition, based on the total weight of the first part of thecomposition.
 10. The composition of claim 8, wherein the core-shellrubber particles have an average particle size of from about 50 μm toabout 300 μm, such as from about 100 μm to about 200 μm, for examplefrom 100 μm to about 150 μm.
 11. The composition of claim 1, wherein thecyanoacrylate component comprises H₂C═C(CN)—COOR, wherein R is selectedfrom alkyl, alkoxyalkyl, cycloalkyl, alkenyl, aralkyl, aryl, allyl andhaloalkyl groups.
 12. The composition of claim 1, wherein the cationiccatalyst comprises salts of lithium and metals from Group II of thePeriodic Table, and non-nucleophilic acids.
 13. The composition of claim1, wherein the cationic catalyst is a non-nucleophilic acid having a pHof less than 1.0 when measured as a 10% by weight solution in water. 14.The composition of claim 1, wherein the cationic catalyst is a memberselected from the group consisting of fluoroboric, fluoroarsenic,fluoroantimonic and fluorophosphoric acids; lithium tetrafluoroborate,calcium di-tetrafluoroborate, magnesium di-tetrafluoroborate, lithumhexaflourophosphate, calcium di-hexaflourophosphate, magnesiumdi-hexaflourophosphate, lithium hexaflouroantimonate and lithiumhexaflouroarsenate; lanthanide triflate salts, aryl iodonium salts, arylsulfonium salts, lanthanum triflate, ytterbium triflate,trimethoxyboroxine, trimethoxyboroxine-aluminum acetyl acetonate,amine-boron trihalide complexes, quaternary ammonium salts, quaternaryphosphonium salts, tri-aryl sulfonium salts, di-aryl iodonium salts, anddiazonium salts; trialkoxyboroxine curing agents; and combinationsthereof.
 15. The composition of claim 1, wherein the cationic curablecomponent is selected from an epoxy component, an episulfide component,an oxetane component, a vinyl ether component and combinations thereof.16. The composition of claim 1, wherein the cationic curable componentis an epoxy component selected from the group consisting ofcycloaliphatic epoxy, aromatic epoxy, aliphatic epoxy and hydrogenatedaromatic epoxy.
 17. The composition of claim 1, wherein the epoxycomponent comprises a member selected from the group consisting ofepoxy-functionalized hydrogenated bisphenol-A, bisphenol-F, bisphenol-E,bisphenol-S and biphenyl.
 18. The composition of claim 1, wherein thefirst part is housed in a first chamber of a dual chamber syringe andthe second part is housed in a second chamber of the dual chambersyringe.
 19. The composition of claim 1, wherein the first part furthercomprises phosphoric acid.
 20. The composition of claim 1, wherein thesecond part further comprises at least one of a plasticizer, a fillerand a toughener.
 21. The composition of claim 20, wherein the tougheneris a member selected from the group consisting of (1) (a) reactionproducts of the combination of ethylene, methyl acrylate and monomershaving carboxylic acid cure sites, (2) (b) dipolymers of ethylene andmethyl acrylate, (3) combinations of (a) and (b), (4) vinylidenechloride-acrylonitrile copolymers, (5) and vinyl chloride/vinyl acetatecopolymer, (6) copolymers of polyethylene and polyvinyl acetate, andcombinations thereof.
 22. The composition of claim 1, wherein the firstpart and the second part are present in a ratio of about 1:1 by volume.23. The composition of claim 1, wherein the first part and the secondpart are each housed in a separate chamber of a dual chamberedcontainer.